This invention relates to a fast search device in a magnetic recording and reproducing device such as an R-DAT (rotary head type digital audio tape recorder) performing fast search for detecting a desired reproducing position during fast feeding or rewinding of a recorded tape and, more particularly, to a fast search device of this type capable of reading information for fast search (i.e., start ID, music number, time data etc.) recorded on the tape in a stable manner from the start of the search.
The R-DAT is a device which converts analog signals such as an audio signal into PCM signals, records the PCM signals on a magnetic tape and reproduces the same.
As shown in FIG. 2, the device comprises a rotary drum 2 having two magnetic heads A and B separated by 180 degree interval on the circumferential surface of a cylinder 1. A tape 3 is loaded from a cassette housing 4 with a vertical post 5 or with an inclined post 6, wound on the circumferential surface of the rotary drum 2 for 90 degrees, supported by a fixed guide 7, and run by a capstan 8 and a pinch roller 9.
The diameter of the rotary drum 2 is 30 mm, and the winding angle for the tape is 90 degrees. For recording and reproduction, at the mode I which is usually used, the rate of the rotary drum 2 is 2,000 rpm (circumferential speed: 3.14 m/sec) and the speed of the tape 3 at 8.15 mm/sec in the direction identical to that of the rotary drum 2. The relative speed of the drum 2 as against the tape 3 is 3.13 m/sec.
The recording system with R-DAT is a helical scanning azimuth recording. Its tape format as shown in FIG. 3 defines with the track angle of 6.degree. 22' 59.5" (during running of the tape) and azimuth angle of .+-.20.degree. with the tracks alternately traced by two heads A and B.
In a track format, audio data are recorded at the center of a PCM region in the longitudinal direction of the track, and sub-codes and control signals such as ATF (automatic track finding) are recorded on both sides thereof.
The PCM region comprises 128 blocks each of which has recording regions for a block synchronizing (indicating the starting position of the block), ID (identification) code, block address, parity check code, and audio data. At the mode I, audio data uses 2's complement codes of quantization bit of 16 bits of the sampling frequency of 48 kHz, and the PCM data is divided into 8 bits in higher order and 8 bits of lower order, modulated from 8 bits into 10 bits (8-10 modulation) and recorded in 10 bits.
In the sub-code region (8 blocks), data such as start ID, music number and time data are recorded. An example of a format in the sub-code region (for one block) is shown in FIG. 4. The start ID is recorded by recording "1" for 9 seconds consecutively at the beginning of a music. By detecting this start ID, fast search designating a specified number of music counted from the current position is enabled. It is also possible to perform fast search depending upon absolute position information such as music number and time data.
For tracking control during reproducing in the R-DAT, an automatic tracking system with ATF is employed. ATF system detects and compares crosstalks from two adjacent tracks by ATF signals (FIG. 5) recorded on the tracks, and controls the speed of the capstan motor for running tape so as to make crosstalks identical. By this arrangement, the head A is caused to trace a track whose azimuth is +20.degree. (hereinafter referred to as A track) and the head B is caused to trace a track whose azimuth is -20.degree. (hereinafter referred to as B track). These heads A and B can respectively trace a width which is about one and half times each track width.
In a magnetic recording and reproducing device such as R-DAT, it will be very convenient if information recorded on the tape can be reproduced even partially during fast feeding (feeding of the tape at a speed which is higher than a normal playback speed) or rewinding (feeding of the tape in a reverse direction to the normal playback direction).
In an R-DAT, for example, it is important for designing the system as a convenient one to have capability of reading data such as present music number and time information recorded on the sub-code region during search (i.e., operation for detecting a desired music number or position in the music). Particularly, in fast search which is conducted at a high speed such as 200 times as fast as the normal speed, it will be extremely difficult to detect a desired tape position unless such data can be read in a stable manner.
In fast search in an R-DAT, the head traces plural tracks, crossing these tracks obliquely as shown in FIG. 6 and passes over a sub-code region of one of these tracks in one crossing. If the relative speed between the head and tape is deviated largely from predetermined relative speed (3.13 m/sec in the case of R-DAT), reproduction of clock cannot be made even if a signal is obtained from the head and, as a result, a sub-code cannot be read. For reading a sub-code, it is necessary for the relative speed between the tape and head to be within a range in which clock can be reproduced (i.e., range in which the relative speed can be subjected to the PLL control for reproduction of clock).
In the prior art device, in a case where fast search is conducted at a speed of, e.g., 200 times as fast as the normal rotation speed, the rotation speed of the rotary drum and rough speed of the tape for realizing the 200 times speed are respectively set (e.g., 3026 rpm for the rotary drum and 1.63 m/sec. for the tape) and, using these values as target values, the rotation speed of the tape reel is finely adjusted after reaching of the target values of the drum motor and the reel motor thereby obtaining the predetermined relative speed.
According to this prior art start control for fast search, a control for matching the relative speed to a predetermined speed is not made in a transient state in starting the drum motor and the reel motor and, for this reason, a signal cannot be read in the transient state. Accordingly, when fast search is conducted designating a certain music number from the current position by utilizing the start ID, the start ID may pass during this transient state so that the start ID is overlooked (since the start ID passes only in 0.9 second in a music of, e.g., 3 minutes if fast search is conducted at a speed 200 times as fast as the normal speed, possibility of such overlooking of the start ID is very high) with a result that a music which is different from the designated one is located. In fast search depending upon absolute position information such as music number and time data also, the target position tends to pass during the transient state and, in this case, search must be made again by running the tape reversely resulting in taking much time for the search.
It is, therefore, an object of the invention to provide a fast search device in a magnetic recording and reproducing device which has eliminated the above described disadvantage of the prior art fast search device and is capable of reading position information for fast search recorded on the tape even in a transient state at the beginning of the search.